The present invention relates to field of document printing and copying. More particularly, it relates to an apparatus for rotatably supporting image-recording and image-transfer drums in spaced parallel relationship while being able to adjust the spacing between the drums.
Automated electrophotographic copiers and printers have been known for nearly fifty years. Copiers and printers differ only from an input standpoint, copiers being adapted to receive hard copy input, whereas printers are adapted to receive an input in electronic form, e.g., from a computer terminal. Both carry out the basic electrophotographic imaging process of uniformly charging a photoconductive layer with electrostatic charge, imagewise exposing the charged layer to radiation adapted to discharge the layer, thereby leaving behind a latent charge image, and applying pigmented electroscopic particles (toner) to the charge image to render it visible. Most often, the toner image so formed is transferred to a receiver sheet whereupon the toner image is permanentized by heat and/or pressure. Optionally, for example, to extend the lifetime of the photoconductive recording element, the toner image formed on the image-recording drum is transferred to an intermediate transfer drum or the like before it is again transferred to the receiver sheet. In the case of full color copying and printing, multiple color-separated toner images (e.g., cyan, magenta, yellow and black) are produced by the above process and transferred in registration to a receiver sheet.
Since the inception of electrophotographic printers/copiers, the xe2x80x9choly grailxe2x80x9d for many manufacturers has been to produce images of photographic quality, both monochromatic and full color. As will be appreciated, the quality of a full color image is determined not only by the respective qualities of each of the color-separated toner images formed on the photoconductive recording element(s), but also by the degree with which such images can be transferred from the recording element(s) and brought into perfect registration on the image receiver sheet. Such image quality of the color-separated images and the registration thereof, in turn, depend in large part upon the precision with which the various work-stations or subsystems that carry out the electrophotographic process can be physically placed relative on the surface of the recording element. Thus, various schemes have been proposed and used in the past that address this technical problem.
While focusing on image-quality and registration issues, printer manufacturers are ever mindful of lowering manufacturing and service costs. Thus, substantial efforts have been made to simplify service and maintenance procedures so that the need for service calls by highly trained technicians and specialists can be minimized. Ideally, for example, all of the major workstations of the printer, e.g. the charging, exposure, development, transfer and cleaning stations, as well as the recording element itself, should be replaceable by the end user or customer with no sacrifice being made to the ultimate image quality. Even where the services of a trained technician are required, the time to implement such replacements should be minimal. The achievement of this goal not only requires that each of the printer work-stations be modularized so as effect a xe2x80x9cplug and playxe2x80x9d concept, but also requires that a very precise and highly reliable work station-registration scheme be designed so that each work station, upon being removed from the printer frame for servicing and/or replacement, can be returned to within a few microns of its nominal position. In the case of high quality color printing, the respective placements of the printer workstations is particularly critical and skilled servicing personnel are usually required to make the major subsystem changes. Obviously, the need for service assistance should be minimized.
In the above-referenced U.S. application Ser. No. 09/474,352, a work station registration scheme for an electrophotographic printer is disclosed in which a plurality of dowel pins on the printer frame serve to locate both a photoconductive drum assembly and an image transfer drum assembly. Each drum assembly comprises a pair of drum-support members, commonly referred to as xe2x80x9cspiders,xe2x80x9d located at opposite ends of the drum. Each spider contains a centrally located bearing for rotatably supporting a drum axle, and a plurality of outwardly extending mechanical fiducials, e.g. bullet-shaped members, which are adapted to mate with complimentary structure, e.g., V-notched blocks, mounted on each work station to precisely locate and space the work-stations relative to the drum""s photoconductive surface. When it comes time to replace the image-recording and/or transfer drums, the work-stations are retracted from their respective positions adjacent the drum surface, thereby providing clearance for drum removal, and the entire drum assembly, including the spider members, are slid axially through an opening in the front wall of the printer frame. The entire drum assembly is then returned to the manufacturer""s facility where the assembly is disassembled and a new drum can be substituted for the worn drum. To install a new drum assembly, the reverse process is carried out, the drum assembly being moved axially inward into the printer frame, until the spiders engage and are seated upon the dowel pins. Thereafter, the workstations are moved toward the drum surface and their respective operative positions. In a similar manner, each of the individual work-stations may be removed from the printer housing, leaving behind, when the drum assembly has been removed, a frame that is totally void of any major components. Only the registration dowel pins remain in the frame, and the entire printer can be reassembled with great precision based on the location of these pins.
While the above-described apparatus fulfills the work station-registration needs for high quality color printing, it may be viewed as a relatively costly and labor-intensive solution. For example, to replace the drum surface, the entire drum assembly, which including the relatively costly drum-support members (spiders) and axles, must be replaced. This requires removal of a relatively heavy subsystem from the printer housing and shipment of such subsystem back to the manufacturing for refurbishing. Since most of the drum assembly components do not require replacement, these components undergo unnecessary shipping and handling during which time they may be damaged or have parts misaligned. This disadvantage is exacerbated by the weight of such components. Ideally, only those components of the drum assemblies that actually need replacement (typically the outermost layer of the drum) should be removed from the printer housing and the remaining components should stay in place for the life of the printer.
In the above-referenced U.S. patent application Ser. No. 09/574,425, there is disclosed a document printer of the above type in which a front drum-support member that normally serves to rotatably support both the image-recording and image-transfer drums is selectively decoupleable from these drums so that the respective outer surfaces of the drums may be serviced and/or replaced while the remaining portions of the drums remain within the printer frame. Such a drum support comprises a pair of double-acting, air cylinder-operated clamps, each being adapted to either grasp or release one of the two opposing axle bearings on each of the drums. When the clamps operate to grasp the axle bearings of the drums, the front drum-support member cooperates with a rear drum-support member to rotatably support the two drums and to properly position the various workstations of the printer relative to the respective outer surfaces of the drums. When the clamps operate to release the axle bearings, the front drum support can be moved, via an articulated mounting mechanism, between its operative position and a standby position within the machine frame that is sufficiently remote from the drums as not to interfere with drum servicing. In such a system, it may be appreciated that the rear drum-support member must be capable not only of supporting the two drums in a cantilever fashion when the front drum-support member is decoupled and moved away from the drums, but also of supporting at least one of the drums for relative movement towards and away from the other so that the so that drums may be brought into pressure contact during the printing operation, and spaced apart during periods of non-use or servicing.
In view of the foregoing discussion, an object of this invention is to provide an improved apparatus for supporting a drum in a cantilever fashion while moving it in a direction substantially parallel to its intended axis of rotation.
Another object of this invention is to provide a printing apparatus in which a pair spaced parallel drums of the type described are rotatably supported and movable relative to each other so that the respective outer surfaces of the drums may be spaced apart or moved into pressure contact.
According to one aspect of the invention, a cantilever drum-mounting apparatus comprises a housing having an opening therein; a carriage movably mounted within the opening and adapted to receive, retain and rotatably support an axle of a drum, such axle defining an axis for drum rotation; and a plurality of guide rollers mounted on the carriage and engagable with an outer surface of the housing to limit movement of the carriage to a direction substantially normal to the axis for drum rotation. Preferably, movement of the carriage is controlled by an air cylinder mounted on the housing and having a movable actuator that cooperates with one or more reference surfaces within the housing opening to locate the drum axle at a desired position.
According to another aspect of the invention, the cantilever drum-mounting apparatus of the invention is used in a document printer/copier to rotatably support an image-transfer drum and to control the position of such drum relative to the surface of an image-recording drum. Thus, according to this aspect of the invention, a document printer/copier comprises: (i) a frame; (ii) an image-recording drum having a photo-sensitive outer surface and having an outwardly extending axle disposed on an intended axis of drum rotation, such axle supporting a first bearing by which the image-recording drum is rotatably supportable; (iii) a plurality of work-stations for producing transferable images on the drum""s photo-sensitive outer surface; (iv) an image-transfer drum having an abhesive outer surface to which toner images previously formed on the image-recording drum are transferable upon being brought into contact with the photo-sensitive outer surface, such image-transfer drum also having an outwardly extending axle disposed on an intended axis of drum rotation, such axle supporting a second bearing by which the image-transfer drum is rotatably supportable; and (v) a drum-support member mounted on the frame and comprising (1) a housing defining (a) a first opening adapted to receive and retain the first bearing at a predetermined location within the first opening, and (b) a second opening spaced from the first opening; (2) a carriage movably mounted on the housing at a location within the second opening for movement toward and away from the first opening, such carriage being adapted to receive and retain the second bearing; and (c) a selectively energizeable actuator for moving the carriage in the second opening to control the spacing between the two drums.
As indicated above, an advantageous technical effect of the invention is that one of the two drum-supports (i.e., the front drum support) disclosed in the above-referenced U.S. patent application Ser. No. 09/574,425 can be decoupled and displaced from the drum axles without disturbing the positional relationship between the image-recording and image-transfer drums. Both drums are supported in parallel positions at all times. While supported at one end only, the image-transfer drum may be lowered or displaced to a position spaced from the image-transfer drum to enable the front drum support to be de-coupled and removed from the drum axles and, after the front drum support has been returned to its operative position, the image-transfer drum can be returned to its operative position, parallel to and in pressure contact with the image-recording drum.
The invention and its advantages will be better understood from the ensuing detailed description of preferred embodiments, reference being made to the accompanying drawings in which like reference characters denote like parts.